Electrical joint structure including aluminum wire and copper connector



March 4, 1969 c. F. LATTER 3,431,547

ELECTRICAL JOINT STRUCTURE INCLUDING ALUMINUM WIRE AND COPPER CONNECTOR Filed Nov. 21. 1966 INVENTOR. CHARLES E LATTEI? BY 'Mj f 7%.

Eila

nited States Patent 3,431,547 ELECTRICAL JOINT STRUCTURE INCLUDING ALUMINUM WIRE AND COPPER CONNECTOR Charles F. Latter, Brampton, Ontario, Canada, assignor to Square D Company, Park Ridge, Ill., a corporation of Michigan Filed Nov. 21, 1966, Ser. No. 595,973 Claims priority, application Canada, May 2, 1966 959,316 US. Cl. 339-272 1 Claim Int. Cl. H01r 7/14 ABSTRACT OF THE DISCLOSURE Molded case circuit breakers rated at and amperes at 120 volts are mounted in panelboards and are used to protect branch electrical circuits in homes and small commercial buildings. Each of the circuit breakers is equipped with a load connector generally comprising a hollow body or housing having a path or channel for receiving an end portion of a wire and a set screw threaded through an opening in a wall of the housing so as to intersect the channel and engage the end portion of the wire and clamp it against the opposite wall of the housing. Each of the panelboards in which the circuit breakers are mounted includes a so-called neutral bar connector for making a common connection between return wires from several branch circuits and a neutral supply wire. A neutral bar comprises a bar or a folded strip of metal having spaced wire-receiving openings or channels each intersected by the inner end portion of a clamping screw. Most of such load connectors and neutral bar connectors are intended for use only with copper wire. The copper wire adequately resists the force of the screw and a good electrical and mechanical connection between the wire and the connector results.

Because of relative price levels and relative availability of copper and aluminum, it has recently become desirable to be able to substitute aluminum wire for copper wire for the branch circuits in homes and small commercial buildings, but it has been found that aluminum wire of the sizes used for carrying 15 and 20 amperes cannot be used with the screw-type connectors designed for use with copper wire. This is principally because aluminum is softer than copper and the screw indents the aluminum wire to the extent that the aluminum wire is easily broken. In addition, aluminum is subject to cold flow so that its shape changes after a time interval and it oxidizes rapidly presenting an insulating surface to the connector. Thus, a connection between a screw-type connector and an aluminum wire which might be mechanically strong and of relatively low resistance when originally made becomes mechanically weak and of relatively high resistance later.

For economy in manufacture and other reasons, the continued use of the present load connectors of circuit breakers and the present neutral bar connectors is desirable. The electrical joint structure of this invention enables aluminum wire to be used in such connectors without breaking, loosening, or overheating.

For safety and economy, an electrical connection 3,431,547 Patented Mar. 4, 1969 should remain relatively cool when carrying its rated current. A connection is considered satisfactory with respect to temperature rise by standard tests if its temperature does not increase more than a predetermined amount above ambient temperature-upon subjection of the connector to a cycling test, each cycle including a period during which current flows through the connector followed by a period during which no current flows, the current being of a magnitude to cause a predetermined increase in the temperature of the connector during the first cycle. In addition to the maximum temperature rise limitation, there must be no sharp temperature rise during the cycling test. The electrical joint structure of this invention enables an aluminum wire to be clamped by a screw in a connector designed for copper wire with the resulting connection meeting all of the foregoing tests as well as standard pull-out tests.

An object of this invention is to provide an improved termination for an aluminum wire that enables a good mechanical and electrical connection to be made by clamping the wire by the inner end face of a screw against a wall of a housing.

Another object is to provide an improved termination for an aluminum wire comprising a copper or copperalloy tube telescoped snugly over an end portion of the wire.

Another object is to provide an improved termination for an aluminum wire comprising a copper or copperalloy tube having an annular flange at only one end and telescoped snugly over an end portion of the Wire with the flanged end of the tube disposed inwardly of the unflanged end of the tube along the end portion of the wire.

Another object is to provide an improved method for securing an aluminum wire in a connector having a set screw intersecting a wire-receiving channel for clamping the wire against a wall of the channel.

Other objects and advantages of this invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is an elevational view of a molded case circuit breaker with a portion of a wall broken away to show a Wire termination in accordance With this invention received in a load connector;

FIG. 2 is an enlarged sectional view of the wire termination and load connector of FIG. 1;

FIG. 3 is a perspective view of a tube and the end portion of an aluminum wire aligned for assembly to form the wire termination of FIGS. 1 and 2; and

FIG. 4 is a perspective view of the wire termination of FIGS. 1 and 2 after removal from a connector in which it has been clamped.

Referring to FIGS. 1 and 2, a copper terminal strap 10 of a molded-case circuit breaker 11 of low ampere rating has an end portion bent back upon itself to define a closed loop or housing 12, a tang 14 of reduced width at the outer end of the strap 10 entering a complementary slit 15 in the strap 10 and being bent as shown to maintain the loop 12. A set screw 16 threaded into an opening in a wall 18 of the loop 15 extends toward an opposite wall 19. Aligned wire-receiving openings 20 and 21 in op posite side walls 24 and 25, respectively, of the loop 12 form a wire-receiving path or channel intersecting the axis of the screw 16.

When a wire termination in accordance with this invention is used, a satisfactory electrical connection between the load connector thus constructed on the end of the terminal strap 10 and an insulated solid or stranded aluminum wire 26 can be made. To make the wire termination, an end portion 28- of the wire 26 from which insulation 29 and any oxide has been removed is inserted into a central opening 30 of a cylindrical copper or copper-alloy tube 31 having an annular flange 32 at one end. The wire termination thus formed is inserted in the aligned openings 20 and '21 with the flange 32 of of the tube 31 serving as a stop to determine the extent of the entry of the wire 26 and the tube 31 into the openings 20 and 21. The screw 16 is then turned to move inwardly toward the wall 19. The inner end face of the screw 16 engages the tube 31 clamping it against the wall 19. During this operation, the tube 31 and the end portion 28 of the wire 26 are deformed slightly, as shown in FIGS. 2 and 4. The tube 31 prevents the screw 16 from making a sharp indentation in the end portion 28 and at the same time distributes the clamping pressure over a relatively large area of the end portion 28, thus preventing breakage of the wire and reducing the effect of any cold flow. The tube 31 also reduces the tendency for oxide to form on the end portion 28. Preferably, the diameter of the wire 26 and the inner diameter of the tube 31 are so related that the tube 31 may be forced over the end portion 28 by finger pressure and retained in assembled position on the end portion 28 by friction between the engaged cylindrical surfaces. The radial thickness of the wall of the tube 31 is preferably much less than the diameter of the wire.

Conveniently, the tubes 31 may be commercially available hollow copper rivets of selected sizes that can be pressed with finger pressure over the end portions of aluminum wires of various diameters, respectively. Preferably, the tubes 31 are plated with tin to reduce electrolytic corrosion problems that occur when copper and aluminum are in direct contact.

Although the invention has been described as used with a load connector of a circuit breaker, its manner of use with neutral bars and other similar connectors is apparent.

I claim:

1. An electrical joint structure including an aluminum wire and a copper connector, the connector having a clamping screw and first and second pairs of spaced opposed wall portions, the wall portions of the first pair extending generally perpendicularly to the wall portions of the second pair, one wall portion of the first pair having a threaded opening, the wall portions of the second pair respectively having a pair of aligned openings adjacent the other wall portion of the first pair, and the clamping screw being threaded into the opening in the one Wall portion of the first pair, and the aluminum wire having an uninsulated free end portion and a copper tube received snugly over the free end portion, the copper tube and the free end portion of the aluminum wire being received in the aligned openings of the second pair of wall portions of the connector and clamped against the other wall portion of the first pair by the clamping screw, and the copper tube having a flange portion on the end thereof farthest from the respective extreme end of the aluminum wire, the flange portion engaging the outer surface of one of the wall portions of the second pair adjacent the opening therein and limiting the extent of insertion of the aluminum wire and copper tube into the aligned openings.

References Cited UNITED STATES PATENTS 2,811,706 10/1957 Logan. 2,907,977 10/1959 Daley. 3,046,512 7/ 1962 Remke et al 339272 X 3,076,954 2/1963 Stanback. 3,309,647 3/1967 Von Holtz 339189 X FOREIGN PATENTS 711,165 10/1941 Germany. 941,846 11/1963 Great Britain. 288,559 5/1953 Switzerland.

MARVIN A. CHAMPION, Primary Examiner. PERRY TEITELBAUM, Assistant Examiner.

US. Cl. X.R. 

